The disclosure relates to powder metallurgical (PM) nickel-base superalloys. More particularly, the disclosure relates to such superalloys used in high-temperature gas turbine engine components such as turbine and compressor disks and other rotor sections.
The combustion, turbine, and exhaust sections of gas turbine engines are subject to extreme heating as are latter portions of the compressor section. This heating imposes substantial material constraints on components of these sections. One area of particular importance involves blade-bearing turbine disks. The disks are subject to extreme mechanical stresses, in addition to the thermal stresses, for significant periods of time during engine operation.
Exotic materials have been developed to address the demands of turbine disk use. U.S. Pat. No. 4,579,602 (the '602 patent) discloses a nickel-base superalloy and processes for powder metallurgical (PM) manufacture of turbine disks. U.S. Pat. No. 6,521,175 (the '175 patent) discloses a further nickel-base superalloy for PM manufacture of turbine disks. The '175 patent discloses disk alloys optimized for short-time engine cycles, with disk temperatures approaching temperatures of about 1500° F. (816° C.). The disclosures of the '602 and '175 patents are incorporated by reference herein in their entirety as if set forth at length.
US Patent Application Publication 20100008790 (the '790 publication) discloses a nickel-based superalloy having a relatively high concentration of tantalum coexisting with a relatively high concentration of one or more other components. 20130209265 (the '265 publication) discloses a more recent alloy. Other disk alloys are disclosed in U.S. Pat. Nos. 5,104,614, 5,662,749, 6,908,519, EP1201777, and EP1195446. The disclosure of said patents and publications are incorporated by reference herein in their entirety as if set forth at length.
In an exemplary PM process, the powdered alloy is compacted into an initial cylindrical precursor (compact). The compact may be wrought processed to reduce cross-sectional area into a billet for, and subsequently forged to form a forging. The forging may then be machined to clean up features or define features (e.g., disk slots for blade root retention). The forged/machined precursor may be heat treated to precipitation harden to increase strength to optimize overall mechanical strength. The forging may be further machined to a shape more closely resembling the finished part configuration. A peening process may then impart a compressive residual stress to prevent fatigue initiation on the surface (particularly in high-fatigue areas).
Coarse grain Ni-based PM superalloys such as described above are ideal candidates for rotating parts, such as disks and hubs in the hot sections of a gas turbine engine because these materials retain their high strengths and creep capability at elevated temperatures. In many cases, multiple stages need to be joined together. Typical joining comprises a bolt circle through two adjacent components. To improve engine operating efficiencies and to reduce engine weight, it is desirable to shift from bolted configurations. Unfortunately, the factors that make these coarse grain alloys good candidates for elevated temperature applications (retention of strength at elevated temperatures) make them extremely difficult to weld and attain acceptable weld joint properties. Current technology attempts to weld the coarse grain material as is, through pre-heating, and through more controlled direct drive/inertia (hybrid) welding systems. See U.S. Pat. No. 5,111,990. These methods do not alter the microstructure to improve weldability.